The invention concerns a hairspring arrangement intended in particular for use in electric watches, with a hub and a hairspring, connected to which is an electric conductor extending over at least a part of its length, insulated against the hairspring, the inner end of which is fastened in a groove in the hub.
A hairspring arrangement of the aforementioned type is already known from the German Patent Specification No. 1,078,677, whereby the hairspring is constructed of three flat layers, namely of two electrically conducting strips and an insulating strip arranged between them, connecting both the conductor strips. The hub or hairspring hub consists of an insulating bushing pushed onto the balance wheel axis, and two metallic ring-halves surrounding same, which between them form a slit-shaped groove which takes up the one end of the hairspring, so that the conductor strips thereof come in contact with the ring-halves of the hub which are electrically insulated from each other. This known hairspring arrangement possesses not only the disadvantage of a comparatively complicated hub-construction which requires a considerable time-consuming assembly, but when fastening the hairspring in the hub particular care must be taken that the conductor strips, which one endeavors to construct as thin as possible, are not damaged.
The invention is based on the task of improving the hairspring arrangement of the aforementioned type in such a way, that a simpler construction of the hub and a simpler fixation of the hairspring to the hub is the result. For this purpose it is proposed to fix the hairspring in a groove of the hub in such a way that the hairspring protrudes from the groove, and furthermore, the protruding part of the hairspring should carry the electric conductor. The basic conception of the invention makes it possible to fix the hairspring, which has the customary shape of an upright standing metal strip, to the hub in the usual way; normally one of the front surfaces of the hub is equipped with a straight or ring-shaped notch which reaches to the peripheral area of the hub and into which the inner end of the hairspring is inserted and then is fastened in the hub by deforming the notch-rims. Up to now the chosen depth of the notch was at least equal to the height of the metal strip forming the hairspring, now, according to invention, the height of the upright standing and hairspring-forming metal band is chosen larger than the depth of the notch arranged on one of the front surfaces of the hub, so that one longitudinal edge of the hairspring protrudes from the hub. If the electric conductor is then arranged on this longitudinal edge of the hairspring--naturally by interpositioning of an insulation layer, e.g. an insulating adhesive--then only the actual hairspring is contacted by the hub, but not the electric conductor carried by the hairspring. The invention, therefore, makes it possible to use a hub of simple construction and to manage with the customary production methods and production means. It would also be possible to use a hairspring of different cross-section and to arrange the notch in a different place on the hub, without having to deviate from the basic concept of the invention.
The construction of the hairspring arrangement in accordance with the invention, with a hairspring protruding from a front surface of the hub makes it possible to make an electric contact with the electric conductor of the hairspring in a particularly simple and practical manner; with a preferred type of construction of the invention, a contact element, especially a contact spring, carried by the balance wheel, rests against the electric conductor in the area of the staked, inner hairspring end. When, as is customary with electric watches, the balance wheel carries a coil, then the one end of this can be connected via a contact spring to the electric conductor carried by the hairspring, without having to connect firmly hub and balance wheel. Therefore, the balance wheel can still be moved in relation to the hairspring arrangement, which can be of advantage for adjustment purposes.
Also at the outer end of the hairspring can by analogous use of the basic concept of the invention an electric contact be made very simply to the electric conductor carried by the hairspring: the outer hairspring end fixed to a fastening point protrudes for this purpose at least with the electric conductor from the fastening point, so that no short-circuiting can happen and the electric conductor carried by the hairspring, via a contact element touching the latter, particularly a contact spring, can be connected to a voltage source, e.g. the drive circuit of an electric watch.
The effective length of a hairspring in watches is usually adjusted via an adjustment lever, swiveling around the balance wheel axis, which has a window through which the hairspring extends. In order to prevent a short-circuit between the electric conductor carried by the hairspring and the mass, for instance an insulating adjustment lever of synthetic material could be used, which is unusual, however. It is proposed, therefore, to construct the window of the adjustment lever in such a way, that it widens in the area of the electric conductor of the hairspring, and at least that window-edge-area faced by the electric conductor carries an insulating layer.